The present invention relates to a high frequency circuit and a high frequency module incorporating the same, and especially relates to technology which is effective for improving the accuracy of compensation operation when compensating, through digital control, variations of the amplification characteristic of a high-frequency power amplification transistor employed in a high-frequency power amplifier circuit, due to variations in a semiconductor manufacturing process.
From the past, a MOS transistor and a bipolar transistor have been employed for a power amplification transistor of an RF power amplifier mounted in a transmitter of wireless communication terminals, such as a mobile-phone. In order to improve the amplification characteristic of a power amplification transistor, it is effective to reduce the channel length of a MOS transistor and the base width of a bipolar transistor.
However, the channel length of a MOS transistor and the base width of a bipolar transistor vary due to variations of the semiconductor manufacturing process, etc. of the MOS transistor and the bipolar transistor. Consequently, when the channel length L of a MOS transistor varies, channel conductance β of the MOS transistor varies, or when the base width Wb of a bipolar transistor varies, an effective base width varies by the Early effect and a collector current changes; accordingly, it is likely that the stability of a high-frequency power amplification characteristic will be impaired.
Patent Literature 1 cited below discloses a high-frequency power amplifier circuit includes an amplification transistor, a current simulation transistor, and a bias generating circuit, in which the bias generating circuit supplies the amplification transistor and the current simulation transistor with a bias for suppressing changes due to the short channel effect or the Early effect, by comparing a voltage generated on the basis of a current which flows through the current simulation transistor, with a reference voltage generated by converting a current of a constant current circuit with a current-to-voltage conversion element.
Patent Literature 2 cited below discloses an amplifier includes a bias unit, an amplifier unit, a current detecting element, a reference current generating unit, and a current comparator unit. The bias unit includes a reference transistor and a replica amplification transistor. A first bias current of the reference transistor and a second bias current of the replica amplification transistor are supplied to the current detecting element. The current detecting element generates a detection current corresponding to a difference between the first bias current and the second bias current. The current comparator unit controls the second bias current of the replica amplification transistor so that the detection current of the current detecting element coincides with the reference current of the reference current generating unit.    (Patent Literature 1) Japanese Patent Laid-open No. 2005-123861    (Patent Literature 2) Japanese Patent Laid-open No. 2010-263405